The invention relates to an inflatable support for the prevention and treatment of pressure sores.
Pressure sores are a condition of progressive tissue death caused primarily by the combination of pressure and shear forces on the human body particularly in the regions of the bony prominences such as ischials, trochanter and heels. These forces act by reducing or stopping the microcirculatory function bringing fresh nutrients (including oxygen) to and removing waste products from the soft tissues underlying the skin. Pressure sores are always debilitating, can often be fatal and even with optimum intervention take from weeks to months to completely heal. The resulting costs for a developed nation (including NATRA, EU, Australasia, Japan) range from £100 m to £600 m annually.
Pressure relieving or reducing supports are provided both in mattress form for lying on and seat product form supporting the buttocks and sometimes the back in operation. All of these support products use different technologies but can be put into two categories by the way they deal with the problem of lowering the pressures imposed on the vulnerable bony prominences (which are at highest risk of pressure sores) by supporting the weight of the human body.
These pressures must be reduced below those that compromise or stop altogether the functions of the capillary bed of the microcirculation in delivering nutrients and removing waste products. For a healthy person this is approximately 32 mmHg but at the capillary bed exits the pressure can be as low as 12-14 mmHg for some persons.
Pressure reducing products work by moulding themselves around the shape of that part of the human body in contact with them, creating the largest contact area and therefore lowering the contact pressures. The technologies used include foam, static air filled bags, gel filled bags, water mattresses and waterbeds. These may be used alone or in combination and include fluidising fine silica beads to create a liquid like substance supporting the body by Archimedes principle of upthrust and displacement balance used for burns patients.
However typical human skin area is 1.8 m2 and in a supine back lying position at most half of this could be contact area so this limits the ultimate pressure reduction.
The alternative concept is that of pressure relief where the part of the body in contact with the mattress or seating product is supported only partially with the contact points being removed in location over time by raising and lowering each part of the product in a predetermined sequence. This principle is invariably implemented using air to inflate or deflate bladders called cells within the product in the predetermined sequence required. Such products are commonly referred to as alternating air products. These static or alternating air based pressure sore mattress and seating products form the largest and most clinically effective (in alternating form) part of all such products.
The pressures imposed by an air mattress on the body are called interface pressures and are a function of the internal or operating pressure of the system. If internal pressure is too low than the parts of body supported touch the base below. But too high a pressure and pressure sores may develop. The majority of people associate lower pressures with more comfort. Patient perception of comfort is important to obtain high compliance and optimum sleep patterns for faster healing.
It is known that operating pressure has to be optimised for an individual patient and is dependent on spatial distribution of patient body density over the area in contact with the mattress or seating product and varies with each patient and their position on the mattress.
Because the bodies"" average density varies considerably between trunk (low average density) and other parts such as heels (high average density) many air products are divided into separate sections or zones each with a different operating pressure.
In order to get optimum pressure reduction or relief, a number of such products, even multi-zoned, use manual operating pressure settings relying entirely on the user or carer for appropriate adjustment.
However, manual operating pressure control raises many problems, namely, it is labour intensive within the hospital, it is not practical in nursing homes and particularly homecare as there are no trained staff present and may be vulnerable to inadvertent mis-setting to ineffective or unsafe positions. Furthermore, apart from gap setting (see below) there is no guide to the right value to guarantee no bottoming and balance good clinical efficacy with acceptable comfort to the patient.
Gap setting adjustment involves setting operating pressure to get clearance of two or three fingers width or palm thickness between the lowest part of the patients body and the mattress or seat base. This is physically intrusive for the patient and difficult or impossible with most mattress designs due to obstructions of parts of the inflated structure.
Some alternating systems provide semi-automatic operating pressure setting by means of additional sensors either under the mattress or within the mattress to indicate when the patient is at risk of bottoming and to control the pump to re-inflate the mattress.
However, such systems do not accommodate different positions of the patient on the mattress, are complex and still require the user to set initial operating pressure upon first use. Static systems are known which upon setting of an operating pressure will then maintain the desirable operating pressure dependent on the user""s weight by using look up tables and pressure sensors sensing and adjusting the internal pressure of the mattress. As with the alternating systems, such systems still require the initial pressure to be set by the caregiver or user.
The invention provides a simple system that, among other advantages, removes the need for manual control of the operating pressure of alternating air mattresses or static systems and automatically sets the correct operating pressure upon use by the user; and resets the operating pressure and maintains the same dependent on change of position of the user or mattress.
Accordingly, the invention provides an inflatable support for a user comprising one or more inflatable cells inflated with fluid from a source to a set pressure, means for venting at least one cell through a known restrictor and measuring the pressure change over time, control means converting this pressure change time value into a mathematical coefficient and comparing with known experimental data, and selecting or determining the optimum support pressure and adjusting the source output to provide the optimum support pressure.
An advantage of the invention is that it uses existing cell air and pressure sensors without adding any components into the mattress. There are no sensors in the mattress, thereby any inflatable mattress is suitable for use in practicing the invention.
Preferably, the cell(s) are vented once every cycle of inflation and deflation in an alternating system for continuous monitoring and resetting of the optimum support pressure.
In a preferred embodiment, the means for venting at least one of the cells is actuated during the deflation cycle. Alternatively, the venting means may be actuated during the inflation cycle.
Preferably, the cell air is vented through a series of restrictors, or more preferably a variable restrictor.
Preferably, the control means includes compiled experimental data of pressure decay with time and associated mathematical coefficients for a large number of users with different body anatomies, on different mattresses and cushions and with differing initial set pressures. More preferably, the control means adds new patient anatomy types and corresponding mathematical coefficient not present in the known experimental data.
Preferably, the inflatable support may have an additional anti-bottoming sensor to allow for lower overall operating pressures, for greater user comfort.
The anti-bottoming sensor may comprise a sensor mat as described in commonly-owned European Patent No. 560563, the entire content of which is hereby incorporated by reference.
In a preferred embodiment the inflatable support may be controlled by remote means connected to the control means.